The proposed work will use a combination of immunocytochemical techniques to characterize the sites of action and relationships of receptors responsive to glutamate, the major excitatory neurotransmitter within the retina. The specific aims are: (1) the localization of GluR subunits to cellular and subcellular sites, using light and electron microscopic immunocytochemistry to identify the cells in the cat retina that express subunits of the AMPA, kainate, NMDA and metabotropic types of GluR and to determine the relationship of these receptors to synaptic specializations; (2) comparison of the receptor distribution with the synaptic relationships of defined subpopulations of retinal neurons, using double-label techniques to compare the distribution of GluRs with a variety of neurochemical markers including neurotransmitters, synthetic enzymes, Ca2+-binding proteins, and second messengers, with specific attention being given to how these relationships correlate with the physiological properties of specific cells; and (3) comparison of GluR distribution with Ca2+-binding proteins and Ca2+-dependent second messengers, using double-labeled tissues to determine whether the retinal localizations are consistent with a role for Ca2+-binding proteins and second messengers in regulation or implementation of the functions of GluR subunits.